I've noticed that other contractors use a system on their website in which they list a lot of towns that they service at the bottom of the page, and some of them are links to pages that have the city name inserted into it at various spots. But everything else on the page is the same except for the city name. They do this with about 10-15 cities.

Is this a good idea? If so, how exactly should it be done, what rules should I follow?

Or will this look like duplicate pages to search engines since most of it is the same except for the city name?